Ultrafast Time-and-Space- Domain Holography by Spectral Hole Burning in Dye-Doped Polymers

Certain photochromic materials exhibit at liquid-helium temperature a special property of very high selectivity in frequency dimension. This phenomenon, commonly known as spectral hole burning (SHB), makes it possible to extend conventional spatial-domain optical data storage into the dimensions of frequency and time. We have applied SHB for ultrafast recording of holograms and coherent optical processing on the timescale of 10-12–10-13 s. To achieve ultrafast performance in the time domain, we use special organic dye-doped polymer materials, which provide SHB recording in a broad optical band width of 5–10 THz. In this paper, we discuss recording and playback of holograms of pico- and femtosecond time-and-space-domain signals using dye-doped SHB polymers at liquid-helium temperature. We discuss unusual properties of SHB holograms such as causality-related asymmetry of diffraction and inversion of the time coordinate, ultrafast frequency-domain processing, and associative recall of events

Symmetry Breaking in Pyrrolo[3,2-b]pyrroles: Synthesis, Solvatofluorochromism and Two-photon Absorption

Five centrosymmetric and one dipolar pyrrolo[3,2-b]pyrroles, possessing either two or one strongly electron-withdrawing nitro group have been synthesized in a straightforward manner from simple building blocks. For the symmetric compounds, the nitroaryl groups induced spontaneous breaking of inversion symmetry in the excited state, thereby leading to large solvatofluorochromism. To study the origin of this effect, the series employed peripheral structural motifs that control the degree of conjugation via altering of dihedral angle between the 4-nitrophenyl moiety and the electron-rich core. We observed that for compounds with a larger dihedral angle, the fluorescence quantum yield decreased quickly when exposed to even moderately polar solvents. Reducing the dihedral angle (i.e., placing the nitrobenzene moiety in the same plane as the rest of the molecule) moderated the dependence on solvent polarity so that the dye exhibited significant emission, even in THF. To investigate at what stage the symmetry breaking occurs, we measured two-photon absorption (2PA) spectra and 2PA cross-sections (sigma(2PA)) for all six compounds. The 2PA transition profile of the dipolar pyrrolo[3,2-b]pyrrole, followed the corresponding one-photon absorption (1PA) spectrum, which provided an estimate of the change of the permanent electric dipole upon transition, approximate to 18D. The nominally symmetric compounds displayed an allowed 2PA transition in the wavelength range of 700-900nm. The expansion via a triple bond resulted in the largest peak value, sigma(2PA)=770GM, whereas altering the dihedral angle had no effect other than reducing the peak value two- or even three-fold. In the S0S1 transition region, the symmetric structures also showed a partial overlap between 2PA and 1PA transitions in the long-wavelength wing of the band, from which a tentative, relatively small dipole moment change, 2-7D, was deduced, thus suggesting that some small symmetry breaking may be possible in the ground state, even before major symmetry breaking occurs in the excited state.1111Ysciescopu

Simultaneous multiple-excitation multiphoton microscopy yields increased imaging sensitivity and specificity

<p>Abstract</p> <p>Background</p> <p>Multiphoton microscopy (MPM) offers many advantages over conventional wide-field and confocal laser scanning microscopy (CLSM) for imaging biological samples such as 3D resolution of excitation, reduced phototoxicity, and deeper tissue imaging. However, adapting MPM for critical multi-color measurements presents a challenge because of the largely overlapping two-photon absorption (TPA) peaks of common biological fluorophores. Currently, most multi-color MPM relies on the absorbance at one intermediate wavelength of multiple dyes, which introduces problems such as decreased and unequal excitation efficiency across the set of dyes.</p> <p>Results</p> <p>Here we describe an MPM system incorporating two, independently controlled sources of two-photon excitation whose wavelengths are adjusted to maximally excite one dye while minimally exciting the other. We report increased signal-to-noise ratios and decreased false positive emission bleed-through using this novel multiple-excitation MPM (ME-MPM) compared to conventional single-excitation MPM (SE-MPM) in a variety of multi-color imaging applications.</p> <p>Conclusions</p> <p>Similar to the tremendous gain in popularity of CLSM after the introduction of multi-color imaging, we anticipate that the ME-MPM system will further increase the popularity of MPM. In addition, ME-MPM provides an excellent tool to more rapidly design and optimize pairs of fluorescence probes for multi-color two-photon imaging, such as CFP/YFP or GFP/DsRed for CLSM.</p

Liquid-liquid phase separation of proteins is modulated by amino acids in vitro and in vivo by regulating protein-protein interactions

Liquid liquid phase separation (LLPS) of proteins is an intracellular process that is widely used by cells for many purposes. In living cells (in vivo), LLPS occurs in complex and crowded environments. Amino acids (AAs) are vital components of such environments, occupying a significant fraction of the cellular volume. In this work, we studied the effects of proline and other proteinogenic AAs on the LLPS of proteins, both in test tubes (in vitro) and in cells (in vivo). The effects of proline on the protein-protein interaction (PPI) and LLPS of both bovine serum albumin (BSA, a folded protein) and the low-complexity domain of fused in sarcoma (FUS267, an intrinsically disordered protein) is first established in vitro. Then, the effects of proline and other proteinogenic AAs on the formation of stress granules (SGs) by LLPS in U2OS and HeLa cells are studied. We find that the presence of AAs renders the net interaction between proteins more repulsive (i.e. stabilizes protein solution), thus suppressing protein phase separation in vitro and in vivo. We also show that the formation of SGs is suppressed by AAs using both immunofluorescence and live-cell microscopy. Our study reveals an underappreciated role of cellular AAs in modulating intracellular phase separation. It may find biomedical applications, especially in the treatment of protein aggregation diseases.Comment: 15 pages, 4 figure

Liquid–liquid phase separation of the Golgi matrix protein GM130

Golgins are an abundant class of peripheral membrane proteins of the Golgi. These very long (50–400 nm) rod-like proteins initially capture cognate transport vesicles, thus enabling subsequent SNARE-mediated membrane fusion. Here, we explore the hypothesis that in addition to serving as vesicle tethers, Golgins may also possess the capacity to phase separate and, thereby, contribute to the internal organization of the Golgi. GM130 is the most abundant Golgin at the cis Golgi. Remarkably, overexpressed GM130 forms liquid droplets in cells analogous to those described for numerous intrinsically disordered proteins with low complexity sequences, even though GM130 is neither low in complexity nor intrinsically disordered. Virtually pure recombinant GM130 also phase-separates into dynamic, liquid-like droplets in close to physiological buffers and at concentrations similar to its estimated local concentration at the cis Golgi

On-off-on Control of Molecular Inversion Symmetry via Multi-stage Protonation: Elucidating Vibronic Laporte Rule

The Laporte rule dictates that one- and two-photon absorption spectra of inversion-symmetric molecules should display alternatively forbidden electronic transitions; however, for organic fluorophores, drawing clear distinction between the symmetric- and non-inversion symmetric two-photon spectra is often obscured due to prevalent vibronic interactions. We take advantage of consecutive single- and double-protonation to break and then reconstitute inversion symmetry in a nominally symmetric diketopyrrolopyrrole, causing large changes in two-photon absorption. By performing detailed one- and two-photon titration experiments, with supporting quantum-chemical model calculations, we explain how certain low-frequency vibrational modes may lead to apparent deviations from the strict Laporte rule. As a result, the system may be indeed considered as an on-off-on inversion symmetry switch, opening new avenues for two-photon sensing applications.Ministry of Education and Research, Republic of Estonia (grants PRG661, PRG690, PSG317) European Regional Development Fund (projects TK134 “EQUiTANT” and TK141 “Advanced materials and high technology devices for energy recuperation systems”) Polish National Science Center, Poland (HARMONIA 2018/30/M/ST5/00460) NSF Award 210362

Strongly Polarized π-Extended 1,4-Dihydropyrrolo[3,2-b]pyrroles Fused with Tetrazolo[1,5-a]quinolines

A straightforward route to 1,4-dihydropyrrolo[3,2-b]pyrroles comprised of two electron-withdrawing quinoline or tetrazolo[1,5-a]quinoline scaffolds has been developed. The versatile multicomponent reaction affording 1,4-dihydropyrrolo[3,2-b]pyrroles combined with intramolecular direct arylation enables assembly of these products in just three steps from anilines with overall yields exceeding 30%. The planarized, ladder-type heteroacenes possess up to 14 conjugated rings. These nominally quadrupolar materials exhibit efficient fluorescence with wavelengths spanning most of the visible spectrum from green−yellow for the dyes possessing biaryl bridges and orange−red for the fully fused systems. In many cases, the fluorescence quantum yields are large, the solvatofluorochromic effects are strong, and the fluorescence is maintained even in crystalline state. Analysis of the electronic structure of these molecular architectures using quantum chemical methods suggests that the character and position of the flanking heterocycle determine the shape of HOMO and LUMO and their extension to N-aryl substituents, influencing the values of molar absorption coefficient. An experimental study of the two-photon absorption (2PA) properties has revealed that it occurs in the 700−800 nm range with apparent deviation from the Laporte parity selection rule, which may be attributed to Hertzberg−Teller contribution to vibronically allowed 2PA transition.Polish National Science Center (grants OPUS 2020/37/B/ST4/00017 and HARMONIA 2018/30/M/ST5/00460); Foundation for Polish Science (TEAM POIR.04.04.00-00-3CF4/16-00); European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowka-Curie, grant agreement No 101007804; Interdisciplinary Center for Mathematical and Computational Modeling (ICM) University of Warsaw under computational allocation G95-1734

Investigation of Electron Transfer-Based Photonic and Electro-Optic Materials and Devices

Montanaâs state program began its sixth year in 2006. The projectâs research cluster focused on physical, chemical, and biological materials that exhibit unique electron-transfer properties. Our investigators have filed several patents and have also have established five spin-off businesses (3 MSU, 2 UM) and a research center (MT Tech). In addition, this project involved faculty and students at three campuses (MSU, UM, MT Tech) and has a number of under-represented students, including 10 women and 5 Native Americans. In 2006, there was an added emphasis on exporting seminars and speakers via the Internet from UM to Chief Dull Knife Community College, as well as work with the MT Department of Commerce to better educate our faculty regarding establishing small businesses, licensing and patent issues, and SBIR program opportunities

Ultrafast Time-and-Space- Domain Holography by Spectral Hole Burning in Dye-Doped Polymers

Certain photochromic materials exhibit at liquid-helium temperature a special property of very high selectivity in frequency dimension. This phenomenon, commonly known as spectral hole burning (SHB), makes it possible to extend conventional spatial-domain optical data storage into the dimensions of frequency and time. We have applied SHB for ultrafast recording of holograms and coherent optical processing on the timescale of 10-12–10-13 s. To achieve ultrafast performance in the time domain, we use special organic dye-doped polymer materials, which provide SHB recording in a broad optical band width of 5–10 THz. In this paper, we discuss recording and playback of holograms of pico- and femtosecond time-and-space-domain signals using dye-doped SHB polymers at liquid-helium temperature. We discuss unusual properties of SHB holograms such as causality-related asymmetry of diffraction and inversion of the time coordinate, ultrafast frequency-domain processing, and associative recall of events.</jats:p

Multiphoton spectroscopy: An optical window into molecular electrostatics

Quantitative knowledge about static molecular electric dipole moments is essential for understanding of intramolecular charge transfer as well as nanometer-scale static electric interactions. However, measuring or determining the molecular electrostatic properties with sufficient accuracy remains a challenging task. In our experiments, we measure the femtosecond two-photon absorption spectra- and cross sections of a range of organic- and organometallic chromophores in solution and use these data to determine the electric dipole moment change in corresponding lowest-energy dipole-allowed transition. Good correspondence of our experimental dipole moments with the quantum-chemical calculations as well as reports by other groups using conventional dipole moment measurement methods suggests that quantitative multiphoton spectroscopy may offer all-optical alternative to the traditional techniques such as Stark effect and electrochromism